My invention relates to improvements in rotary plug valves or valve assemblies of the type shown in my U.S. Pat. No. 2,988,319 dated June 13, 1961 comprising (1) a stationary valve body or casing including a main valve chamber having an inlet port and an outlet port communicating with the main valve chamber and (2) a rotary plug member snugly fitting into the main valve chamber, the plug member being provided with a through passage adapted when the plug is in open position to permit flow of fluid through the valve from the inlet port to the outlet port. Means are provided for rotating the valve plug through 90.degree. to the open position from a closed position and vice versa. In order to provide a fluid tight fit, the plug valve and plug valve chamber are correspondingly tapered and preferably provided with sealing rings.
While this arrangement is effective in securing a fluid tight fit, it is difficult to turn the valve plug member and accordingly various means have been provided to overcome this defect.
In accordance with my U.S. Pat. No. 2,988,319, cam means are provided reacting between the valve casing and the rotary valve plug for automatically lifting the valve plug from its seat during rotation of the valve plug to and from the open to the closed position and vice versa.
In my prior patent, I also provide balancing means responsive to fluid pressure in the valve chamber for biasing the valve plug to its seated position against its tendency to become unseated by fluid pressure in said chamber. In spite of these improvements, there still remains a tendency for the tapered valve to stick and resist turning, and the present improvement is designed to reduce this tendency.
In accordance with my invention, I make the valve plug in two parts: one part comprising the tapered valve plug per se which fits in the valve chamber and the other comprising a plug operating head, cap or member provided with suitable actuating means such as an operating handle.
The operating head is provided with cam tracks which may be similar to the cam tracks disclosed in my U.S. Pat. No. 2,988,319 and which cooperate with pins projecting through the valve casing. Initial turning of the operating handle results in a rotary movement of the operating member, head or cap accompanied by a lifting movement due to the cam members which lifting movement is also imparted to the tapered valve plug which is thereby removed from its seat, and sticking eliminated.
The two parts, namely the cap or head and the valve plug are provided with a pin-and-slot connection permitting the operating cap and handle to be turned through a limited angle before rotary motion is imparted to the valve plug per se. Spring means preferably in the form of a pin or bar of spring steel, are also provided, interposed between the operating head or cap and the tapered valve plug. This pin is so arranged as to be stressed or biased during the initial turning movement of the handle and cap.
After the initial rotation of the valve cap relative to the valve plug and the lifting of the cap and plug relative to the casing, the spring means which has been biased due to the relative rotation of the cap and plug now tends to bring the cap and valve plug back to their original position relative to each other, since the valve plug has been lifted from its seat and is now readily rotatable. Continued rotation of the operating handle and cap brings the valve plug to its final open or closed position depending on the direction of the rotation of the operating handle due to the cam action, as set forth in U.S. Pat. No. 2,988,319.
In addition to the pin and slot connection between the valve plug and the operating cap and the spring biasing operation just described, the present device discloses improved details of construction of the valve assembly which include improvements in the balancing piston carried at the end of the valve plug and in the end plate of the cylindrical housing for the balancing piston. These improvements result in easier assembly of the valve parts and the improved operation of the valve assembly as a whole. Other improvements will be apparent from the further description of the invention.
The invention will be more readily understood by reference to the accompanying drawings and the following detailed description and claims.